Zoom lens, camera, and portable information terminal apparatus

ABSTRACT

A lens ( 1 ), a lens ( 2 ) and a lens ( 3 ) constitute a first group of lenses, a lens ( 4 ), a lens ( 5 ), a lens ( 6 ) and a lens ( 7 ) constitute a second group of lenses, and a lens ( 8 ) constitutes a third group of lenses in a zoom lens of the present invention. The second group of lenses is constituted by a first positive lens ( 4 ), a negative lens ( 5 ) which is in a meniscus shape which faces its convex shape toward a side of an object ( 70 ), a second positive lens ( 6 ) in a meniscus shape which faces its convex shape toward the object ( 70 ) side, and the third positive lens ( 7 ), which are in order from the object ( 70 ) side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens, more specifically, to thezoom lens utilizing a plastic aspheric lens.

2. Description of the Prior Art

In recent years, a market for a digital camera is expanding greatly, andthe user's demand for the digital camera have been ranged in scopeaccordingly. That is, needless to say that not only a high image qualityand a miniaturization are demanded, but also the demand for a weightsaving of a zoom lens becomes greater in recent years.

There are considered various types of zoom lenses for the digitalcamera. As a type suited for widening an angle of view and for theminiaturization, there is a zoom lens of type which has a first group oflenses having a negative focal length, a second group of lenses having apositive focal length and a third group of lenses having a positivefocal length which are arranged subsequently from a side of an objectside to a side of an image, and has an aperture stop disposed at theobject side of the second group of lenses that moves integrally with thesecond group of lenses, and in a change of magnification from a shortfocal end to a long focal end, the second group of lenses monotonouslymoves from the image side to the object side and the first group oflenses moves so as to correct a displacement of a position of imageplane in accordance with the change of magnification.

For example, in Japanese Patent Laid Open No. H10-039214, there isdisclosed a small-size zoom lens which a position of an exit pupil canbe separated from an image plane sufficiently, has the wide angle ofview and is blight, has a good performance, and yet, capable of carryingout a large change of magnification ratio. According to the small-sizedzoom lens disclosed in Japanese Patent Laid Open No. H10-039214, it isconstituted by arranging a first group of lenses to a third group oflenses subsequently from the object side to the image side, and thefirst group of lenses has a negative refractive power, the second grouphas a positive refractive power and the third group of lenses has thepositive refractive power. It also has an aperture stop at the objectside of the second group of lenses that moves integrally with the secondgroup of lenses when carrying out a zooming, and the third group oflenses is a fixed group relating to the zooming. At the time of carryingout the zooming from a wide angle end to a telephoto end, the firstgroup of lenses is moved to the image side on an optical axis firstlyand then a direction of its movement is reversed to the object side onthe way so that the first group of lenses is moved to the image side insuch a manner as to draw a convex-like arc shape to correct adisplacement in an focusing position, and the second group of lenses ismoved monotonously to the object side on the optical axis to carry outthe change of magnification.

Also, in Japanese Patent Laid Open 2000-267009, a small sized, highimage quality and inexpensive zoom lens which arranges a plastic lensfor a zoom lens which has a negative-positive two-element zoom lenseffectively and which is particularly suited for a digital still camera,is disclosed. According to the zoom lens disclosed in Japanese PatentLaid Open 2000-267009, at least one of lenses constitutes each group oflenses in a zoom lens having negative-positive-positive three-elementlens seen from the object side is the plastic lens, and it also has astructure which a following conditional formula is satisfied:−0.8<Cp×(N′−N)/φW<0.8−0.45<M3/M2<0.90 (where φT/φW>1.6) where Cp is acurvature of the plastic lens, φW is a power of entire system at thewide angle end, N and N′ are the object side of an aspheric surface andan refraction index of d-line of medium at the image side, M2 and M3show amounts of movements of the second group of lenses and the thirdgroup of lenses respectively (using the wide angle end as the base andsetting the object side as −), and φT is the power of entire system atthe telephoto end.

The above mentioned Japanese Patent Laid Open No. H10-039214 was filedat the earliest time as the above zoom lens of such type, and a basicstructure of the above zoom lens of such type is all

Also, Japanese Patent Laid Open 2000-267009 provides the zoom lensutilizing a plastic aspheric lens. However, the second group of lenseshaving a function of the change of magnification and an imaging functionwhich are most influential on an aberration correction function is atriplets type in the embodiment described in Japanese Patent Laid Open2000-267009, therefore there is a problem that it has no sufficientaberration correction function.

SUMMARY OF THE INVENTION

The present invention has been made in view of the aforementionedproblems, and therefore it is an object of the present invention toprovide a zoom lens which is small sized, light weighted and has a wideangle of view by using a plastic aspheric lens while having highperformance equivalent to or more than conventional zoom lenses.

To accomplish the aforementioned object, a zoom lens according to afirst aspect of the present invention comprises a first group of lenseshaving a negative refractive power, a second group of lenses having apositive refractive power and a third group of lenses having thepositive refractive power, and an aperture stop provided at an objectside of the second group of lenses. In addition, a first positive lens,a negative lens, a second positive lens and a third positive lens aresubsequently arranged from the object side to the image side in thesecond group of lenses. Furthermore, when a zooming from a short focalend to a long focal end is carried out, the second group of lenses ismonotonously moved from an image side to the object side, and the firstgroup of lenses is moved so as to correct a displacement of a positionof image plane in accordance with the zooming, and at least the thirdpositive lens positioned nearest to the image side is a plastic asphericlens.

Also, according to a second aspect of the present invention, thenegative lens is formed by a negative lens in a meniscus shape whichfaces its convex surface toward the object side. In addition, the secondpositive lens is formed by a positive lens in a meniscus shape whichfaces its convex surface toward the object side.

In the zoom lens of the present invention, the first group of lenses tothe third group of lenses are arranged subsequently from the object sideto the image side. The first group of lenses has the “negativerefractive power”, the second group of lenses has the “positiverefractive power” and the third group of lenses has the “positiverefractive power.”The aperture stop provided at the object side of thesecond group of lenses moves integrally with the second group of lenseswhen carrying out the zooming. In addition, when carrying out thezooming from a wide angle end to a telephoto end, the first group oflenses is moved to the image side on an optical axis firstly and then adirection of its movement is reversed to the object side on the way sothat the first group of lenses is “moved to the image side in such amanner as to draw a convex-like arc shape” to correct a displacement inan focusing position, and the second group of lenses is movedmonotonously to the object side on the optical axis, to carry out thechange of magnification. Also, since the aperture stop is movedintegrally with the second group of lenses when carrying out thezooming, the movement of the second group of lenses is not hindered bythe aperture stop. The most characteristic of the present invention isthat at least the third positive lens positioned nearest to the imageside is the plastic aspheric lens.

According to this invention, because the plastic aspheric lens is usedfor the second group of lenses with a conventional structure of the zoomlens, the small sized camera (portable information terminal apparatus)which is lighter weighted and more convenient to use than theconventional ones and capable of widening the angle of view can berealized while having the high performance and in small size equivalentto or more than the conventional ones.

Also, according to a third aspect of the present invention, a followingconditional formula is satisfied:0.08<f ₂ /f _(2p)<0.8

if a focal length of the second group of lenses is f₂, and the focallength of the third positive lens is f_(2p).

By providing the second group of lenses to have two pieces of thepositive lenses to the image side, power can be weakened per one piecein the zoom lens of the present invention. Generally, although theplastic lens is known to have a tendency that the position of imageplane or the like is easily be displaced by an environmental variation,the plastic lens in the present invention becomes difficult to beinfluenced by the environmental variation by introducing such lenshaving relatively weak power, as a result, the widening of angle of viewin photographing angle of view and the weight saving of a lens systemcan be accomplished together. Here, a focal length of the plasticaspheric lens is desired to satisfy the conditional formula described inthe present invention.

According to this invention, since the focal length of the plasticaspheric lens is designed to satisfy the aforementioned conditionalformula, the zoom lens which has the high performance and difficult tobe influenced by the environmental variation even more can be provided.

Also, according to the forth aspect of the present invention, at leastthe negative lens of the second group of lenses and the second positivelens are jointed.

In order to reduce performance degradation by an error in assembling thelens in the zoom lens of the present invention, it is preferred to jointhe negative lens of the second group of lenses with the second positivelens in the image side thereof.

According to this structure, since the negative lens of the second groupof lenses and the second positive lens in the image side thereof arejointed, the zoom lens having simpler structure with less performancedegradation can be provided.

Also, according to a fifth aspect of the present invention, a followingconditional formula is satisfied:0.8<R _(c) /Y _(max)<1.2

if a radius of curvature in a jointed surface of the second group oflenses is R_(c), and a maximum image height is Y_(max).

Although the aberration in directions mutually counteracting at asurface of the image side of the negative lens and at a surface of theobject side of the second positive lens is largely generated andtherefore degradation of image performance by a relative de-centering ofthe two lenses is large, such degradation of image performance can beavoided by joining the negative lens with the second positive lens. Inorder to attain the zoom lens having the high performance even more whenjoining the negative lens with the second positive lens, it is desiredto satisfy the conditional formula in the present invention.

According to this invention, since the design is made to satisfy theconditional formula, the zoom lens having the high performance andsimple structure can be provided.

Also, according to a sixth aspect of the present invention, the aperturestop provided at the object side of the second group of lenses movesintegrally with the second group of lenses, and at least a surface ofthe second group of lenses that is nearest to the object side is anaspheric surface.

To provide the zoom lens of the present invention to be furthersimplified and in high performance even more, it is desired to providethe aperture stop which moves integrally with the second group of lensesat the object side of the second group of lenses and set at least theobject side surface in the lens at nearest to the object side of thesecond group of lenses to be aspheric surface.

According to this invention, because the aperture stop which movesintegrally with the second group of lenses is provided and at least theobject side surface in the lens at the nearest to the object side of thesecond group of lenses is set to be aspheric surface, the zoom lenswhich an aspheric aberration is less can be provided, as a result, thecamera (portable information terminal apparatus) having even higherimage quality can be realized.

Also, according to a seventh aspect of the present invention, at leastone piece of plastic aspheric lens, whose both surfaces thereof areaspheric surfaces, is provided.

Although more aspheric surfaces may be provided in order to improve theaberration correction function even more, if a lens which has theaspheric surfaces on both sides thereof are introduced by using a highdegree of freedom in processing the plastic lens, great effect in termsof efficiency can be attained.

According to this invention, because at least one piece of the plasticaspheric lens is provided, the zoom lens which is superior in theaberration correction function can be provided.

Also, according to an eighth aspect of the present invention, the firstgroup of lenses is provided with a plastic aspheric lens, and the thirdgroup of lenses is provided with a plastic aspheric lens.

A large number of plastic lenses may be used in order to pursue moreweight saving of the zoom lens in the present invention, but there is noso much choice for the plastic which can be used as the lens comparedwith an optical glass in terms of a refraction index and dispersion.Accordingly, the aberration correction function deteriorates if theexcessive plastic lenses are used in the same group of lenses ratherthan raising the aberration correction function. To take a balancebetween the weight saving and the aberration correction functionefficiently while avoiding the deterioration in the aberrationcorrection function, it is preferred to adopt a method in which theplastic aspheric lenses distribute to each of the group of lenses.

More specifically, in one of the zoom lens in the present invention, thethird positive lens which the second group of lenses provides is theplastic aspheric lens, the first group of lenses provides at least oneplastic aspheric lens, and the third group of lenses provides at leastone plastic aspheric lens.

According to this invention, since the plastic aspheric lenses aredistributed to each of the group of lenses, even lighter zoom lens canbe provided.

According to a ninth aspect of the present invention, the zoom lensdescribed in the above first aspect is provided as a photographingoptical system.

According to this invention, since the zoom lens which can beminiaturized even more and has the high performance equivalent to ormore than the conventional ones is used for a photographing opticalsystem, the camera which is small in size and has the high image qualitycan be provided, as a result, the user can photograph the high qualityimage by using the camera which is superior in portability.

Also, according to a tenth aspect of the present invention, the zoomlens described in the first aspect is provided as a photographingoptical system of a camera function section.

According to this invention, because the zoom lens which can beminiaturized even more and has the high performance equivalent to ormore than the conventional ones is used for a photographing opticalsystem of the camera function section, the portable information terminalapparatus which is small in size and has the high image quality can beprovided, as a result, the user can photograph the high quality image byusing the portable information terminal apparatus which is superior inportability, and can transmit the photographed image to outside.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a structure of a zoom lens inan embodiment of numeric value 1 of the present invention.

FIG. 2 is a cross sectional view showing a structure of a zoom lens inan embodiment of numeric value 2 of the present invention.

FIG. 3 is a cross sectional view showing a structure of a zoom lens inan embodiment of numeric value 3 of the present invention.

FIG. 4 is an aberration curve diameter in a short focal end of the zoomlens in the embodiment of numeric value 1 of the present invention.

FIG. 5 is an aberration curve diameter in a middle focal length of thezoom lens in the embodiment of numeric value 1 of the present invention.

FIG. 6 is an aberration curve diameter in a long focal end of the zoomlens in the embodiment of numeric value 1 of the present invention.

FIG. 7 is an aberration curve diameter in the short focal end of thezoom lens in the embodiment of numeric value 2 of the present invention.

FIG. 8 is an aberration curve diameter in the middle focal length of thezoom lens in the embodiment of numeric value 2 of the present invention.

FIG. 9 is an aberration curve diameter in the long focal end of the zoomlens in the embodiment of numeric value 2 of the present invention.

FIG. 10 is an aberration curve diameter in the short focal end of thezoom lens in the embodiment of numeric value 3 of the present invention.

FIG. 11 is an aberration curve diameter in the middle focal length ofthe zoom lens in the embodiment of numeric value 3 of the presentinvention.

FIG. 12 is an aberration curve diameter in the long focal end of thezoom lens in the embodiment of numeric value 3 of the present invention.

FIG. 13 is an outside view showing one embodiment as a camera (portableinformation terminal apparatus) of the present invention.

FIG. 14 is a block diagram of an inner structure showing one embodimentas the camera (portable information terminal apparatus) of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a specific description of the present invention will beexplained by using embodiments shown in the accompanying drawings.However, components, types, combinations, configurations or theirrelative arrangements which are described in the present embodiments arenot intended to limit the scope of the present invention, rather, theyare merely explanatory examples unless otherwise specifically stated.

As shown in FIGS. 1 to 3, generally in a zoom lens constituted by threegroups of lenses L, M and N which are arranged bynegative-positive-positive subsequently in this order, the second groupof lenses M monotonously moves from a side of an image 80 to a side ofan object 70 in such a manner shown by an arrow B when a change ofmagnification from a short focal end to a long focal end is carried out,and the first group of lenses L is moved in such a manner shown by anarrow A so as to correct displacement of a position of image plane inaccordance with the change of magnification. The second group of lensesM plays a role in most of a function of the change of magnification, andthe third group of lenses N is provided mainly for separating an exitpupil away from an image plane. In order to promote furtherminiaturization in the zoom lens of such, a power in each of the groupof lenses, particularly the power in second group of lenses M which isas a group of change of magnification, has to be enhanced. Accordingly,a fine aberration correction is required to be carried out in the secondgroup of lenses M.

In the present invention, as referring to FIG. 1, the second group oflenses M is constituted by a first positive lens 4, a negative lens 5, asecond positive lens 6 and a third positive lens 7 subsequently from theobject 70 side in order. Particularly in the present embodiments, theaforementioned negative lens 5 is formed as a negative lens in ameniscus shape which faces its convex surface toward the object 70 side,and the aforementioned second positive lens 6 is formed as a positivelens in the meniscus shape which faces its convex surface toward theobject 70 side. Although this composition is based on so-called atriplets structure which the positive lenses are arranged at both sidesof the negative lens, a degree of freedom of correction in an off axisaberration is increased by dividing into the positive lenses 6 and 7 atthe image 80 side which an off axis light departs from an optical axis.Accordingly, it is possible to correct a coma aberration and astigmatismor the like effectively even if a photographing angle of view is turnedinto wide angle of view.

Also, by dividing into the positive lenses 6 and 7 which are at theimage 80 side, a power per one piece can be weakened. Generally,although a plastic lens is known to have a tendency that the position ofimage plane or the like is easily be displaced by an environmentalvariation, the plastic lens in the present invention becomes difficultto be influenced by the environmental variation by introducing such lenshaving relatively weak power, as a result, the widening of angle of viewin photographing angle of view and weight saving of lens system can beaccomplished together. Here, a focal length of a plastic aspheric lensis desired to satisfy a following conditional formula:0.08<f ₂ /f _(2p)<0.8

where f₂ represents the focal length of the second group of lenses M,and f_(2p) represents the focal length of the plastic aspheric lens inthe second group of lenses M that is nearest to the image 80 side. Inaddition, if f₂/f_(2p) becomes below 0.08, the power in the plasticaspheric lens becomes relatively too small, and therefore, there is notso much point in adding the lenses. If f₂/f_(2p) becomes over 0.8, thelens becomes such a lens that easily be influenced by the environmentalvariation because of the power being relatively too strong, andtherefore, the fine aberration correction becomes difficult to becarried out. It is further desirable to satisfy a following conditionalformula:0.1<f ₂ /f _(2p)<0.7

Also, in order to reduce performance degradation by an error inassembling the lens in the zoom lens of the present invention, it ispreferred to join the negative lens 5 which is in the meniscus shape ofthe second group of lenses M with the second positive lens 6 which is inthe meniscus shape of the image side thereof. More specifically,although the aberration in directions mutually counteracting at asurface of the image 80 side of the negative lens 5 and at a surface ofthe object 70 side of the second positive lens 6 is largely generatedand therefore degradation of image performance by a relativede-centering of these two lenses is large, such degradation of imageperformance can be avoided by joining the negative lens 5 with thesecond positive lens 6, that is, joining the both meniscus lenses. Inorder to attain the zoom lens having the high performance even more whenjoining the both meniscus lenses, it is desired to satisfy a followingconditional formula.0.8<R _(c) /Y _(max)<1.2

where R_(c) represents radius of curvature in the jointed surface,Y_(max) represents a maximum image height, respectively. However, whenR_(c)/Y_(max) is below 0.8, then the power at the jointed surfacebecomes too large and as a result, the aberration becomes difficult tobe balanced, and when R_(c)/Y_(max) is over 1.2, the power at thejointed surface becomes too small, as a result, the sufficientaberration correction function cannot be obtained. Therefore, the fineaberration correction becomes difficult to be carried out in both ways.It is further desirable to satisfy a following conditional formula:0.9<R _(c) /Y _(max)<1.1

Also, to provide the zoom lens of the present invention to be furthersimplified and in high performance even more, it is desired to providean aperture stop 9 which integrally moves with the second group oflenses M at the object 70 side of the second group of lenses M and setat least the surface of the object 70 side in the first positive lens 4nearest to the object 70 side of the second group of lenses M to beaspheric surface. More specifically, since the surface of the secondgroup of lenses M at the nearest to the object 70 side is in proximityto the aperture stop, and a marginal light has sufficient height andalso a change in height of light by a zooming is less, it is possible tocorrect a spherical aberration which is a basis of an imagingperformance more finely by providing the aspheric surface at theaforementioned surface of the second group of lenses M at the nearest tothe object 70 side.

In addition, although more aspheric surfaces may be provided in order toimprove the aberration correction function even more, if a lens havingthe aspheric surfaces on both sides thereof is introduced by using ahigh degree of freedom in processing the plastic lens, great effect interms of efficiency can be attained.

Also, a large number of plastic lenses may be used in order to pursuemore weight saving of the zoom lens in the present invention, but thereis not so much choice for the plastic which can be used as the lenscompared with an optical glass in terms of refraction index anddispersion. Accordingly, the aberration correction function deterioratesif the excessive plastic lenses are used in the same group of lensesrather than raising the aberration correction function. To take abalance between the weight saving and the aberration correction functionefficiently while avoiding the deterioration in the aberrationcorrection function, it is preferred to adopt a method in which theplastic aspheric lenses distribute to each of the group of lenses fromthe first to the third groups of lenses. That is, it is preferred forthe weight saving if the third positive lens which the second group oflenses M provides being provided as the plastic aspheric lens, and atleast one piece among the second group of lenses L being provided as theplastic aspheric lens and at least one piece among the third group oflenses N being provided as the plastic aspheric lens.

Specific embodiments of numeric values according to the zoom lens of thepresent invention are shown hereunder. The aberrations in the presentembodiments are sufficiently corrected, thereby making it possible tocorrespond to a light receiving element of 2,000,000 pixels to 4,000,000pixels. By constituting the zoom lens as in the present invention, it ispossible to accomplish the fine image performance while achieving asufficient miniaturization. Also, in any one of the embodiments, thelens 2 of the first group of lenses L, the lens 7 of the second group oflenses M positioned nearest to the image 80 side (that is, the thirdpositive lens) and the lens 8 of the third group of lenses N are plasticaspheric lenses. Furthermore, the second group of lenses M ismonotonously moved from the image 80 side to the object 70 side in sucha manner shown by the arrow B, and the first group of lenses L is movedin such a manner shown by the arrow A so as to correct the displacementof the position of image plane in accordance with the change ofmagnification.

Meaning for signs in each embodiment are as follows.

f: Focal length of entire system

F: F number

ω: Half angle of view

R: Radius of curvature

D: Face interval

N_(d): Refraction index

υ_(d): Abbe number

K: Conical constant of aspherical surface

A₄: Fourth-order aspherical coefficient

A₆: Sixth-order aspherical coefficient

A₈: Eighth-order aspherical coefficient

A₁₀: Tenth-order aspherical coefficient

A₁₂: Twelfth-order aspherical coefficient

A₁₄: Fourteenth-order aspherical coefficient

A₁₆: Sixteenth-order aspherical coefficient

A₁₈: Eighteenth-order aspherical coefficient

The aspherical surface used here is defined in the following formula:X={CH ²/1+√{square root over ( )}(1−(1+K)C ² H ²)}+A ₄ ·H ⁴ +A ₆ +A ₈ ·H⁸ +A ₁₀ ·H ¹⁰ +A ₁₂ ·H ¹² +A ₁₄ ·H ¹⁴ +A ₁₆ ·H ¹⁶ +A ₁₈ ·H ¹⁸

where an inverted number of a proximal axis curvature radius (proximalaxis curvature) is C, and the height of the optical axis is H.

FIG. 1 is a cross sectional view showing the structure of the zoom lensin the first embodiment of the present invention. The zoom lens in thefirst embodiment of the present invention is constituted by a lens 1, alens 2, a lens 3, the first positive lens 4, the negative lens 5 in themeniscus shape, the second positive lens 6 in the meniscus shape, thethird positive lens 7, the lens 8, the aperture stop 9 and a filter 10,which are arranged from the object side 70 to the image 80 side. Inaddition, the lens 1, the lens 2 and the lens 3 constitute the firstgroup of lenses L, the first positive lens 4, the negative lens 5, thesecond positive lens 6 and the third positive lens 7 constitute thesecond group of lenses M, and the lens 8 constitutes the third group oflenses N. The embodiment of numeric value of those will be describedhereunder.

[Embodiment of numeric value 1] f = 5.97–16.88, F = 2.76–4.54 ω =39.20–15.32 Surface No. R D Nd νd Remarks 01 20.817 1.67 1.77250 49.62Lens 1   02 7.903 3.31 First group 03 −244.273 1.61 1.53048 55.78 Lens 2{close oversize brace} of lenses L  04* 9.234 2.74 05 17.550 2.141.71740 29.50 Lens 3 06 −592.689 Variable (A) 07 aperture stop 1.00  08*8.831 1.75 1.74330 49.33 First positive lens 4 09 31.256 0.54 Second 1014.025 3.67 1.84700 23.80 Negative lens 5 group of 11 5.000 2.95 1.4875070.44 Second positive lens 6 {close oversize brace} lenses M 12 56.8910.11 13 69.906 2.82 1.53048 55.78 Third positive lens 7  14* −216.903Variable (B)  15* 29.711 1.62 1.53048 55.78 Lens 8 } Third group oflenses N 16 −133.022 Variable (C) 17 ∞ 3.32 1.51680 64.20 Variousfilters 18 ∞Aspherical Surface; Fourth Surface

K=0.0, A4=−0.286310×10⁻³, A6=−0.500552×10⁻⁵, A8=0.418669×10⁻⁶A10=−0.246109×10⁻⁷, A12=0.613238×10⁻⁹, A14=−0.179780×10⁻¹¹A16=−0.200092×10⁻¹², A18=0.266967×10⁻¹⁴

Aspherical Surface; Eighth Surface

K=0.0, A4=−0.756502×10⁻⁴, A6=−0.714045×10⁻⁶, A8=0.772288×10⁻⁸A10=−0.759411×10⁻⁹

Aspherical Surface; Fourteenth Surface

K=0.0, A4=0.363652×10⁻³, A6=0.113628×10⁻⁴, A8=0.796657×10⁻⁶A10=0.384502×10⁻⁷

Aspherical Surface; Fifteenth Surface

K=0.0, A4=−0.959689×10⁻⁴, A6=0.496504×10⁻⁻⁵, A8=−0.221147×10⁻⁶A10=0.425230×10⁻⁸

Variable Interval

Short focal end middle focal length long focal end f = 5.97 f = 10.05 f= 16.88 A 21.264 8.776 1.500 B 2.913 7.525 15.720 C 3.610 3.605 3.101Value of Conditional Formulaf ₂ /f ₂=0.144R _(c) /Y _(max)=1.075

FIG. 4 is an aberration curve diameter in the short focal end of thezoom lens according to the embodiment of numeric value 1, FIG. 5 is anaberration curve diameter in the middle focal length of the zoom lensaccording to the embodiment of numeric value 1, and FIG. 6 is anaberration curve diameter in the long focal end of the zoom lensaccording to the embodiment of numeric value 1.

FIG. 2 is a cross sectional view showing a zoom lens in a secondembodiment of the present invention. The zoom lens in the secondembodiment of the present invention is constituted by a lens 11, a lens12, a lens 13, a first positive lens 14, a negative lens 15 which is inthe meniscus shape, a second positive lens 16 in the meniscus shape, athird positive lens 17, a lens 18, an aperture stop 19 and a filter 20,which are arranged from the object 70 side to the image 80 side. Inaddition, the lens 11, the lens 12 and the lens 13 constitute the firstgroup of lenses L, the first positive lens 14, the negative lens 15, thesecond positive lens 16 and the third positive lens 17 constitute thesecond group of lenses M, and the lens 18 constitutes the third group oflenses N. The embodiment of numeric value of those will be describedhereunder.

[Embodiment of numeric value 2] f = 5.97–16.88, F = 2.78–4.47 ω =39.13–15.48 Surface No. R D Nd νd Remarks 01 14.775 1.21 1.80420 46.50Lens 11   02 7.448 3.77 First group  03* 56.813 1.41 1.53048 55.78 Lens12 {close oversize brace} of lenses L  04* 8.551 3.06 05 17.779 1.881.84666 23.78 Lens 13 06 50.274 Variable (A) 07 aperture stop 1.00  08*7.718 1.75 1.74330 49.33 First positive lens 14 09 18.026 1.00 Second 1013.857 3.39 1.80518 25.46 Negative lens 15 group of 11 4.650 3.761.48749 70.44 Second positive lens 16 {close oversize brace} lenses M 1224.198 0.50  13* 14.578 3.00 1.58910 61.30 Third positive lens 17  14*122.346 Variable (B)  15* 10.918 1.58 1.53048 55.80 Lens 18 } Thirdgroup of lenses N 16 16.371 Variable (C) 17 ∞ 3.33 1.51680 64.20 Variousfilters 18 ∞Aspherical Surface; Third Surface

K=0.0, A4=−0.210448×10⁻³, A6=0.504148×10⁻⁵, A8=−0.242816×10⁻⁷A10=−0.656401×10⁻¹⁰,

Aspherical Surface; Fourth Surface

K=0.0, A4=−0.549100×10⁻³, A6=−0.135386×10⁻⁵, A8=0.453082×10⁻⁶A10=−0.260541×10⁻⁷, A12=0.587680×10⁻⁹, A14=−0.113968×10⁻¹¹A16=−0.192632×10⁻¹², A18=0.236265×10⁻¹⁴

Aspherical Surface; Eighth Surface

K=0.0, A4=−0.889606×10⁻⁴, A6=−0.165729×10⁻⁵, A8=0.46209079×10⁻⁷,A10=−0.247332×10⁻⁸

Aspherical Surface; Thirteenth Surface

K=0.0, A4=−0.487327×10⁻³, A6=−0.141052×10⁻⁴, A8=−0.540166>×10⁻⁶,A10=0.375653×10⁻⁸

Aspherical Surface; Fourteenth Surface

K=0.0, A4=−0.161674×10⁻³, A6=−0.859375×10⁻⁵, A8=−0.733020×10⁻⁶,A10=0.244131×10⁻⁷

Aspherical Surface; Fifteenth Surface

K=0.0, A4=−0.785817×10⁻⁴, A6=0.108028×10⁻⁵, A8=−0.655020×10⁻⁷,A10=0.131296×10⁻⁸

Variable Interval

Short focal end middle focal length long focal end f = 5.97 f = 10.05 f= 16.88 A 21.111 8.942 1.606 B 1.926 6.892 14.611 C 3.290 3.100 3.100Value of Conditional Formulaf ₂ /f _(2p)=0.464R _(c) /Y _(max)=1.000

FIG. 7 is an aberration curve diameter in the short focal end of thezoom lens according to the embodiment of numeric value 2, FIG. 8 is anaberration curve diameter in the middle focal length of the zoom lensaccording to the embodiment of numeric value 2, and FIG. 9 is anaberration curve diameter in the long focal end of the zoom lensaccording to the embodiment of numeric value 2.

FIG. 3 is a cross sectional view showing a zoom lens in a thirdembodiment of the present invention. The zoom lens in the thirdembodiment of the present invention is constituted by a lens 21, a lens22, a lens 23, a first positive lens 24, a negative lens 25 in themeniscus shape, a second positive lens 26 in the meniscus shape, a thirdpositive lens 27, a lens 28, an aperture stop 29 and a filter 30. Inaddition, the lens 21, the lens 22 and the lens 23 constitute the firstgroup of lenses L, the first positive lens 24, the negative lens 25, thesecond positive lens 26 and the third positive lens 27 constitute thesecond group of lenses M, and the lens 28 constitutes the third group oflenses N. The embodiment of numeric value of those will be describedhereunder.

[Embodiment of numeric value 3] f = 5.97–16.88, F = 2.75–4.57 ω =39.20–15.32 Surface No. R D Nd νd Remarks 01 20.625 1.78 1.77250 49.62Lens 21   02 7.896 3.50 First group  03* −257.596 1.66 1.53048 55.78Lens 22 {close oversize brace} of lenses L 04 9.380 2.79 05 17.958 2.211.71736 29.50 Lens 23 06 4031.046 Variable (A) 07 aperture stop 1.00 088.784 1.80 1.74330 49.33 First positive lens 24 09 31.431 1.00 Second 1012.803 3.44 1.84666 23.78 Negative lens 25 group of 11 4.614 3.761.48749 70.44 Second positive lens 26 {close oversize brace} lenses M 1210.170 0.31  13* 9.785 1.92 1.53048 55.78 Third positive lens 27 1455.076 Variable (B)  15* 31.377 2.10 1.53048 55.78 Lens 28 } Third groupof lenses N 16 −61.392 Variable (C) 17 ∞ 3.33 1.51680 64.20 Variousfilters 18 ∞Aspherical Surface; Fourth Surface

K=0.0, A4=−0.282506×10⁻³, A6=−0.509455×10⁻⁵, A8=0.421360×10⁻⁶A10=−0.245536×10⁻⁷, A12=0.613289×10⁻⁹, A14=−0.181872×10⁻¹¹A16=−0.200488×10⁻¹², A18=0.267509×10⁻¹⁴

Aspherical Surface; Eighth Surface

K=0.0, A4=−0.751881×10⁻⁴, A6=−0.769572×10⁻⁶, A8=0.848299×10⁻⁸,A10=−0.802058×10⁻¹⁰

Aspherical Surface; Thirteenth Surface

K=0.0, A4=0.813495×10⁻⁶, A6=0.717205×10⁻⁷, A8=−0.819604×10⁻⁸A10=0.304697×10⁻⁷

Aspherical Surface; Fourteenth Surface

K=0.0, A4=0.342223×10⁻³, A6=0.805437×10⁻⁵, A8=−0.819604×10⁻⁸A10=0.304697×10⁻⁷

Aspherical Surface; Fifteenth Surface

K=0.0, A4=−0.984535×10⁻⁴, A6=0.484064×10⁻⁵, A8=−0.199016×10⁻⁶,A10=0.343781×10⁻⁸

Variable Interval

Short focal end middle focal length long focal end f = 5.97 f = 10.05 f= 16.88 A 20.787 8.684 1.501 B 2.251 7.135 15.268 C 3.412 3.302 3.100Value of Conditional Formulaf ₂ /f _(2p)=0.655R _(c) /Y _(max)=0.992

FIG. 10 is an aberration curve diameter in the short focal end of thezoom lens according to the embodiment of numeric value 3, FIG. 11 is anaberration curve diameter in the middle focal length of the zoom lensaccording to the embodiment of numeric value 3, and FIG. 12 is anaberration curve diameter in the long focal end of the zoom lensaccording to the embodiment of numeric value 3.

FIGS. 13A, 13B and 13C are perspective views of a camera which uses thezoom lens of the present invention. FIG. 13A is the perspective viewseen from front, FIG. 13B is the partial perspective view which aphotographing lens 54 is zoomed, and FIG. 13C is the perspective viewseen from back. The camera has the photographing lens 54 and a lightreceiving element (area sensor) which is not shown, and the camera isconstituted so as to read out an image of a subject formed by thephotographing lens 54 by the light receiving element. The zoom lensdescribed in the embodiment of the present invention is used as thephotographing lens 54. When the camera is carried, the photographinglens 54 is in a sunken state as shown in FIG. 13A, and when the usersupplies power by operating a power switch 57, a lens barrel is extendedout as shown in FIG. 13B. At this time, each group of lenses of the zoomlens inside of the lens barrel is, for example, disposed in the shortfocal end. The disposition of each of the group of lenses is changed bycontrolling a zoom lever 52, as a result, the change of magnification tothe long focal end can be carried out. At this time, the change ofmagnification of a viewfinder 50 is also carried out interlocked with achange in the angle of view of the photographing lens 54. In addition, afocusing is performed by a half-pressing of a shutter release button 51.The focusing in the zoom lens described in the present embodiments canbe performed by the movement of the aforementioned first group of lensesor the aforementioned third group of lenses, or a movement of the lightreceiving element. The photographing is performed if the shutter releasebutton 51 is further pressed down. Additionally, an operation button 56is used when displaying the image stored in a semiconductor memory on aliquid crystal monitor 55, or transmitting outside by using a card orthe like. The semiconductor memory and the communication card are usedby respectively inserting into slots 58 and 59 which are exclusive orgeneral-purpose.

FIG. 14 is a block diagram showing an inner structure of a camera 100 inthe present invention. The light receiving element 67 reads out theimage of the subject formed by a photographing lens 66. In addition, anoutput from a light receiving element 67 is processed by a signalprocessing device 65 which is controlled by a central processing unit63, and the processed output is converted into digital information.Image information digitalized by the signal processing device 65 isrecorded on the semiconductor memory 62 after being applied with apredetermined image process in an image processing device 64 which iscontrolled by the central processing unit 63. The liquid crystal monitor60 is capable of displaying the image in photographing and alsodisplaying the image stored in the semiconductor memory 62. Also, theimage stored in the semiconductor memory 62 can be transmitted outsideby use of a communication card or the like 61. By the way, the camera100 is provided with a viewfinder 68 in which the change ofmagnification is carried out interlocked with the change in the angle ofview of the photographing lens 66.

For the camera (portable information terminal apparatus) as describedabove, the zoom lens in the embodiments 1 to 3 of numeric values in acharacter of the lens groups can be used as a photographing lens.Therefore, the small sized, high image quality camera (portableinformation terminal apparatus) which utilizes the light receivingelement of 2,000,000 pixels to 4,000,000 pixels can be realized.

As described above, according to one of the present invention, becausethe plastic aspheric lens is used for the third positive lens of thesecond group of lenses that is nearest to the image side with astructure of a conventional zoom lens, the small sized camera (portableinformation terminal apparatus) which is lighter weighted and moreconvenient to use than the conventional ones and capable of widening theangle of view can be realized while having the high performance and insmall size equivalent to or more than the conventional ones.

Also, according to another one of the present invention, because it isdesigned to satisfy the following conditional formula:0.08<f ₂ /f _(2p)<0.8

if the focal length of the aforementioned second group of lenses is f₂and the focal length of the aforementioned third positive lens isf_(2p), the zoom lens which has the high performance and difficult to beinfluenced by the environmental variation even more can be provided.

Also, according to yet another one of the present invention, because thenegative lens in the meniscus shape of the second group of lenses andthe second positive lens in the meniscus shape of the image side thereofare jointed, the zoom lens having simpler structure with lessperformance degradation can be provided.

Also, according to yet another one of the present invention, because itis designed to satisfy the following conditional formula:0.8<R _(c) /Y _(max)<1.2

if R_(c) is the radius of curvature in the jointed surface of theaforementioned second group of lenses, and Y_(max) is the maximum imageheight, the zoom lens having the high performance and the simplestructure can be provided.

Also, according to yet another one of the present invention, because theaperture stop which moves integrally with the second group of lenses isprovided and at least the object side surface in the lens at the nearestto the object side of the second group of lenses is set to be asphericsurface, the zoom lens which an aspheric aberration is less can beprovided, as a result, the camera (portable information terminalapparatus) having even high image quality can be realized.

Also, according to yet another one of the present invention, because atleast one piece of the plastic aspheric lens is provided, the zoom lenswhich is superior in the aberration correction function can be provided.

Also, according to yet another one of the present invention, because theaforementioned first group of lenses is provided with the plasticaspheric lens and the aforementioned third group of lenses is providedwith the plastic aspheric lens, and thereby the plastic aspheric lensesare distributed to each of the group of lenses, the lighter weightedzoom lens can be provided.

Also, according to yet another one of the present invention, because thezoom lens which can be miniaturized even more and has the highperformance equivalent to or more than the conventional ones is used fora photographing optical system, the camera which is small in size andhas the high image quality can be provided, as a result, the user canphotograph the high quality image by using the camera which is superiorin portability.

Also, according to yet another one of the present invention, because thezoom lens which can be miniaturized even more and has the highperformance equivalent to or more than the conventional ones is used fora photographing optical system of a camera function section, theportable information terminal apparatus which is small in size and hasthe high image quality can be provided, as a result, the user canphotograph the high quality image by using the portable informationterminal apparatus which is superior in portability, and can transmitthe photographed image to outside.

1. A zoom lens, comprising: a first group of lenses, a second group oflenses and a third group of lenses which are subsequently arranged froman object side to an image side; said first group of lenses havingnegative refractive power, said second group of lenses having positiverefractive power and said third group of lenses having positiverefractive power; and an aperture stop provided at the object side ofsaid second group of lenses, wherein when zooming from a short focal endto a long focal end is carried out, said second group of lenses movesmonotonously from the image side to the object side and said first groupof lenses moves so as to correct displacement of an image plane positioncaused in accordance with the zooming, said first group of lensesincludes one positive lens and two negative lenses, said second group oflenses includes three positive lenses and one negative lens, and atleast the positive lens in said second group of lenses positionednearest to the image side is a plastic aspheric lens.
 2. The zoom lensaccording to claim 1, wherein said first group of lenses has thenegative lens, the negative lens and the positive lens subsequentlyarranged from the object side to the image side.
 3. The zoom lensaccording to claim 2, wherein at least one of said two negative lensesin said first group of lenses is a negative meniscus lens.
 4. The zoomlens according to claim 2, wherein both of said two negative lenses insaid first group of lenses are negative meniscus lenses.
 5. The zoomlens according to claim 1, wherein a following conditional formula issatisfied:0.08<f ₂ /f ₂<0.08 where a focal length of said second group of lensesis f₂, and a focal length of said plastic aspheric lens positionednearest to the image side in said second group of lenses is f₂.
 6. Thezoom lens according to claim 1, wherein at least said negative lens ofsaid second group of lenses and one of said three positive lenses ofsaid second group of lenses are jointed.
 7. The zoom lens according toclaim 6, wherein a following conditional formula is satisfied:0.8<R _(c) /Y _(max)<1.2 where a radius of curvature in a jointedsurface of said second group of lenses is R_(c), and a maximum imageheight is Y_(max).
 8. The zoom lens according to claim 1, wherein saidaperture stop provided at the object side of said second group of lensesmoves integrally with the second group of lenses, and at least a surfaceof said second group of lenses nearest to the object side is an asphericsurface.
 9. The zoom lens according to claim 1, wherein at least oneplastic aspheric lens, whose both surfaces thereof are asphericsurfaces, is provided.
 10. The zoom lens according to claim 1, whereinsaid first group of lenses is provided with a plastic aspheric lens, andsaid third group of lenses is provided with a plastic aspheric lens. 11.The zoom lens according to claim 1, wherein said negative lens in saidsecond group of lenses is a negative lens of a meniscus shape having aconvex surface facing toward the object side, and one of said threepositive lenses in said second group of lenses is a positive lens of ameniscus shape having a convex surface facing toward the object side.12. A camera, comprising: a zoom lens as a photographing optical system;said zoom lens being comprised of a first group of lenses, a secondgroup of lenses and a third group of lenses which are subsequentlyarranged from an object side to an image side; said first group oflenses having negative refractive power, said second group of lenseshaving positive refractive power and said third group of lenses havingpositive refractive power; and an aperture stop provided at the objectside of said second group of lenses, wherein when zooming from a shortfocal end to a long focal end is carried out, said second group oflenses moves monotonously from the image side to the object side andsaid first group of lenses moves so as to correct displacement of animage plane position caused in accordance with the zooming, said firstgroup of lenses has one positive lens and two negative lenses, saidsecond group of lenses includes three positive lenses and one negativelens, and at least the positive lens in said second group of lensespositioned nearest to the image side is a plastic aspheric lens.
 13. Aportable information terminal apparatus, comprising: a zoom lens as aphotographing optical system of a camera function section; said zoomlens being comprised of a first group of lenses, a second group oflenses and a third group of lenses which are subsequently arranged froman object side to an image side; said first group of lenses havingnegative refractive power, said second group of lenses having positiverefractive power and said third group of lenses having positiverefractive power; and an aperture stop provided at the object side ofsaid second group of lenses, wherein when zooming from a short focal endto a long focal end is carried out, said second group of lenses movesmonotonously from the image side to the object side and said first groupof lenses moves so as to correct displacement of an image plane positioncaused in accordance with the zooming, said first group of lenses hasone positive lens and two negative lenses, said second group of lensesincludes three positive lenses and one negative lens, and at least thepositive lens in said second group of lenses positioned nearest to theimage side is a plastic aspheric lens.
 14. A zoom lens, comprising: afirst group of lenses, a second group of lenses and a third group oflenses which are subsequently arranged from an object side to an imageside; said first group of lenses having negative refractive power, saidsecond group of lenses having positive refractive power and said thirdgroup of lenses having positive refractive power; and an aperture stopprovided at the object side of said second group of lenses, wherein whenzooming from a short focal end to a long focal end is carried out, saidsecond group of lenses moves monotonously from the image side to theobject side and said first group of lenses moves so as to correctdisplacement of an image plane position caused in accordance with thezooming, said second group of lenses includes three positive lenses andone negative lens, said negative lens in said second group of lenses isa negative meniscus lens having a convex surface facing toward theobject side and one of said three positive lenses in said second groupof lenses is a positive meniscus lens having a convex surface facingtoward the object side, said negative meniscus lens of said second groupof lenses and said positive meniscus lens of said second group of lensesare jointed, and at least the positive lens in said second group oflenses positioned nearest to the image side is a plastic aspheric lens.15. The zoom lens according to claim 14, wherein said first group oflenses has a negative lens, a negative lens, and a positive lenssubsequently arranged from the object side to the image side.
 16. Thezoom lens according to claim 15, wherein at least one of said twonegative lenses in said first group of lenses is a negative meniscuslens.
 17. The zoom lens according to claim 15, wherein both of said twonegative lenses in said first group of lenses are negative meniscuslenses.
 18. The zoom lens according to claim 14, wherein a followingconditional formula is satisfied:0.08<f ₂ /f _(2p)<0.8 where a focal length of said second group oflenses is f₂, and a focal length of said plastic aspheric lenspositioned nearest to the image side in said second group of lenses isf₂.
 19. The zoom lens according to claim 14 wherein a followingconditional formula is satisfied:0.8<R _(c) /Y _(max)<1.2 where a radius of curvature in a jointedsurface of said second group of lenses is R_(c), and a maximum imageheight is Y_(max).
 20. The zoom lens according to claim 14, wherein saidaperture stop provided at the object side of said second group of lensesmoves integrally with the second group of lenses, and at least a surfaceof said second group of lenses nearest to the object side is an asphericsurface.
 21. The zoom lens according to claim 14, wherein at least oneplastic aspheric lens, whose both surfaces thereof are asphericsurfaces, is provided.
 22. The zoom lens according to claim 14, whereinsaid first group of lenses is provided with a plastic aspheric lens, andsaid third group of lenses is provided with a plastic aspheric lens. 23.A camera, comprising: a zoom lens as a photographing optical system;said zoom lens being comprised of a first group of lenses, a secondgroup of lenses and a third group of lenses which are subsequentlyarranged from an object side to an image side; said first group oflenses having negative refractive power, said second group of lenseshaving positive refractive power and said third group of lenses havingpositive refractive power; and an aperture stop provided at the objectside of said second group of lenses, wherein when zooming from a shortfocal end to a long focal end is carried out, said second group oflenses moves monotonously from the image side to the object side andsaid first group of lenses moves so as to correct displacement of animage plane position caused in accordance with the zooming, said secondgroup of lenses includes three positive lenses and one negative lens,said negative lens in said second group of lenses is a negative meniscuslens having a convex surface facing toward the object side and one ofsaid three positive lenses in said second group of lenses is a positivemeniscus lens having a convex surface facing toward the object side,said negative meniscus lens of said second group of lenses and saidpositive meniscus lens of said second group of lenses are jointed, andat least the positive lens in said second group of lenses positionednearest to the image side is a plastic aspheric lens.
 24. A portableinformation terminal apparatus, comprising: a zoom lens as aphotographing optical system of a camera function section; said zoomlens being comprised of a first group of lenses, a second group oflenses and a third group of lenses which are subsequently arranged froman object side to an image side; said first group of lenses havingnegative refractive power, said second group of lenses having positiverefractive power and said third group of lenses having positiverefractive power; and an aperture stop provided at the object side ofsaid second group of lenses, wherein when zooming from a short focal endto a long focal end is carried out, said second group of lenses movesmonotonously from the image side to the object side and said first groupof lenses moves so as to correct displacement of an image plane positioncaused in accordance with the zooming, said second group of lensesincludes three positive lenses and one negative lens, said negative lensin said second group of lenses is a negative meniscus lens having aconvex surface facing toward the object side and one of said threepositive lenses in said second group of lenses is a positive meniscuslens having a convex surface facing toward the object side, saidnegative meniscus lens of said second group of lenses and said positivemeniscus lens of said second group of lenses are jointed, and at leastthe positive lens in said second group of lenses positioned nearest tothe image side is a plastic aspheric lens.